in the field of ultrafast photonics. Since the successful demonstration of graphene-based saturable absorber (SA) for ultrafast pulsed lasers, [7,8] 2D layered materials including black phosphorus, topological insulators, and transition metal dichalcogenides (TMDs), have recently been extensively investigated in nonlinear optical devices for the generation of ultrafast pulses via passive modelocking operation. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] In particular, the recent advancements in the development of TMDs with unique electronic and optical attributes have explored many potential applications in electronics and photonics. [24,25] The TMDs with layered structure can be exfoliated into atomic-thin layers, which advance the development of wider applications as high-performance transistors, photodetectors and nonlinear optical devices owing to their widespread bandgaps from the visible to the nearinfrared region. [24][25][26][27][28][29][30][31] Currently, nonlinear optical devices based on group VIB TMDs have been fully studied using as saturable absorbers (SA) for the successful generation of short pulses in broadband region. [17][18][19][20][21][22][23][32][33][34][35][36] Despite the previous efforts, it is still possible to optimize the SA devices toward ultrafast photonics for the admired purposes of generating laser pulse with shorter pulse width and greater output power, which can be anticipated by exploring other members of TMDs. In comparison with intensively studied group VIB TMDs, group IVB TMDs which are theoretically predicted to have superior physical properties to group VIB TMDs, have rarely been investigated yet. [37,38] For instance, single-layered HfS 2 is expected to possess much higher carrier mobility (≈1800 cm 2 V −1 s −1 ) and smaller bandgap (≈1.2 eV) than that of MoS 2 . [38,39] Owing to superior electronic properties, ultrathin HfS 2 fabricated by mechanically exfoliation or chemical vapor deposition methods presents significant potential in phototransistors and field-effect transistors. [40][41][42][43][44][45][46][47] However, to our knowledge, the nonlinear optical properties of HfS 2 and its application in ultrafast photonics remain unknown.In this contribution, we demonstrate a new function of multilayered HfS 2 nanosheets (NSs) with nonlinear optical absorption for development of ultrafast photonic devices. We prepared HfS 2 NSs via a modified liquid exfoliation approach using isopropanol (IPA) as solvent. HfS 2 dispersions are precisely deposited onto a microfiber to form a SA device by using a photonic crystal fiber (PCF) assisted deposition method. The HfS 2 SA device is found to show excellent nonlinear absorption Group IVB transition metal dichalcogenides (TMDs) have attracted significant interests in photoelectronics due to their predictable superior physical properties compared to group VIB (Mo and W) TMDs. However, the nonlinear optical properties and ultrafast photonic devices based on group IVB TMDs remained unexplored so far. Herein, the nonlinear ...

We demonstrate a bismuth (Bi) saturable absorber (SA) for generating ultrafast pulse. The Bi SA is fabricated by the Bi film deposited on the surface of microfibers through using magnetron sputtering. Its nonlinear optical properties are investigated. The as-prepared Bi SA has outstanding nonlinear absorption property demonstrated by the open aperture (OA) <i>Z</i>-scan system at 1500 nm and balanced twin-detector method at 1560 nm. The nonlinear optical property of Bi SA shows that the modulation depth, the nonsaturable losses, and the saturable intensity at 1.5 μm are 14% and 79%, and 0.9 MW/cm², respectively. Besides, the closed aperture (CA) <i>Z</i>-scan measurement is also implemented to estimate the nonlinear refractive index of Bi film. The Bi film shows that the typical CA/OA curve possesses the feature of peak-valley profile, meaning that the sample with a negative nonlinear refractive index is self-defocusing. In our experiments, the parameters of the nonlinear absorption coefficient <i>β</i> and the nonlinear refractive index <i>n</i>₂ are estimated at about 2.38 × 10^–4 cm/W and –1.47 × 10^–9 cm²/W according to the actual experimental data points, respectively. To further investigate its nonlinear optical property, the microfiber-based Bi SA is embedded into an erbium-doped fiber laser with a typical ring cavity structure. Based on the Bi SA device, the stable ultrafast pulses are generated at 1.5 μm with the pulse width of 357 fs, the output power of 45.4 mW, corresponding to the pulse energy of 2.39 nJ, and the signal-to-noise ratio is 84 dB. The stable soliton pulses emitting at 1563 nm are obtained with a 3-dB and 6-nm spectral bandwidth. The experimental results suggest that the microfiber-based Bi SA prepared by magnetron sputtering deposition (MSD) technique can be used as an excellent photonic device for ultrafast pulse generation in the 1.5 μm regime, and the MSD technique opens a promising way to produce high-performance SA with a large modulation depth, low saturable intensity, and high power tolerance, which are conducible to the generation of high power and ultrafast pulse with high stability.

Cylindrical vector beams (CVBs), with non-uniform state of polarizations, have become an indispensable tool in many areas of science and technology. However, little research has explored high power CVBs at the femtosecond regime. In this paper, we report on the generation of high quality CVBs with high peak power and femtosecond pulse duration in a fiber chirpedpulse amplification laser system. The radially (azimuthally) polarized vector beam has been obtained with a pulse duration of 440 fs (430 fs) and a maximum average output power of 20.36 W (20.12 W). The maximum output pulse energy is ∼20 μJ at a repetition rate of 1 MHz, corresponding to a high peak power of ∼46 MW. The comparison between simulated intensity profiles and measured experimental results suggests that the generated CVBs have a remarkable intensity distribution. The proposed configuration of our laser system provides a promising solution for high quality CVBs generation with the characteristics of high peak power, ultrashort pulse duration, and high mode purity.